Environmental Engineering Reference
In-Depth Information
Superheaters
Chimney
Boiler
Cooling tower
Mechanical
dust arrestors
Conveyor
house
LP
Power station
Generator
transformer
22 kV
Turbine
Generator
HP
Main flue
Coal
bunker
Steam
(trom
boiler)
Cooling
water
(outlet)
Air
Electrical
precipitator
Current to
transformer
Cooling
water (inlet)
Step-up
transformer
Condensed steam
(returned to boiler)
Coal
Condensers
Induced
draught fan
33 kV
Forced
draught fan
Pulverised fuel mill
Step-
down
Bulk power
substation
Transmission
system
Circuit-
breaker
Subtransmission
system
Large industrial consumer
Small
industrial
consumer
132 kV (UK)
230/115 kV
(USA)
400 or 275 kV (UK)
500 or 345 kV (USA)
Distribution
substation
Domestic and commercial consumer
Step-down
transformer
Step-
down
Cable
E
Primary
distribution 11 kV
Secondary distribution
415 V 3-phase
240 V 1-phase (UK)
110 V 1-phase (USA)
Distribution
transformer
Figure 1.12
Pictorial view of the components of a large power system
fi ttings, heat energy by 100% effi cient resistive elements, and power supply to electronic and
IT (information technology) hardware through very effi cient power conditioning units.
Figure 1.12 shows a diagrammatic layout of a typical electrical power system from the
point of generation to the point of consumption. The fi gure depicts a coal fi red power station
as this represents the majority of world stations. The energy conversion chain follows the
chemical
electrical path depicted in Figure 1.8. Coal is pulver-
ized and fed into a boiler where it is mixed with forced air and combusted. The boiler is a
complex structure consisting of many stages of energy extraction from the combusted fuel.
The fl ue gases are guided through equipment that removes solid particles and sulfur (desul-
furization is not shown in the fi gure) before being released into the atmosphere. The highly
purifi ed water in the boiler is converted into superheated steam which is passed through
several turbine stages on the shaft of a turbogenerator. The low pressure low temperature
steam from the outlet of the turbine is condensed into the purifi ed water which in this closed
system is pumped back into the boiler. The condensing process unfortunately needs a sub-
stantial amount of external cooling water. In the fi gure, this water is provided from a pond
at the bottom of a cooling tower. The hot water from the condenser is sprayed at the top of
the tower and transfers its heat to the air that passes up the venturi shaped tower. The lost
water must be made up from some external source such as a local river.
The energy generated at the power stations is transmitted to consumers by overhead trans-
mission lines and underground cables that possess ohmic resistance. The energy loss due to
the unavoidable resistive heating of a line or cable is proportional to the square of the current
I
it carries. Additionally, for a given power transfer, which is proportional to
VI
, the current
is inversely proportional to the voltage (other things being equal). Thus, the loss decreases
→
thermal
→
mechanical
→
